Reverse current relay



C. R. PETER REVERSE CURRENT RELAY May 19, 1959 Filed June 10, 1957 --5/ 30 Mia/ [III/[(155111];

REVERSE CURRENT RELAY Charles R. Peter, Waukesha County, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application June 10, 1957, Serial No. 664,651

7 Claims. (Cl. 317-188) This invention relates generally to relays and specifically to an improved form of reverse current relay.

Various forms of electromagnetic relay devices have been employed to sense a reverse flow of current in an electric circuit, but most of these have been unsatisfactory in one or more respects. For example, a very high forward current will cause some reverse current relays to actuate due to the very great magnetic flux caused by the high current which overrides the reference flux or causes improper core saturations. Elimination of this tendency to actuate a high forward current may be had by sacrificing sensitivity to low values of reverse current or the characteristic which allows the relay to reset itself when the reverse current drops to a low value.

The relay of this invention avoids the shortcomings of prior art devices through the use of three air gaps, two of which are adjustable and serve to set the operating point of the relay. The arrangement of three core legs permits the magnetic flux produced by the current flowing in the measuring conductor to add to the fiux produced by a'reference winding in one leg or another, depending on the direction of current flow. In this manner the relay armature is attracted to a first core leg or a second core leg, depending on the direction of current flow in the conductor.

It is therefore an object of this invention to provide an improved relay.

It is another object of this invention to provide a relay with three air gaps, two of which are adjustable.

It is still another object of this invention to provide a reverse current relay with improved sensitivity and drop out characteristics which are easily adjusted.

Fig. l is a side view, partly in section, of a relay emboclying the invention.

Fig. 2 is a top view of the same relay as Fig. 1.

Fig. 3 is a sectional view taken along III-Ill of Fig. 2.

Fig. 4 is a sectional view taken along IV-IV of Fig. 1.

Fig. 5 is a schematic drawing of the magnetic flux paths for the normal condition.

Fig. 6 is a schematic drawing of the magnetic flux paths for the reverse current condition.

With reference to the drawing, the preferred embodiment of the invention comprises a three legged magnetic core 1 having a reference leg 2, a center leg 3 and a conductor support leg 4 afiixed to a base member 5 by means of suitable screws 7. At the upper end of the conductor leg 4 is an extension of magnetic material 8 fastened to the leg by means of screws 9. The center leg 3 has an extension 10 of magnetic material fastened by means of screws 6. The extensions of the center leg and the conductor leg are held in a fixed relation by means of a spacer 13 made of nonmagnetic material and screws 15 which pass through a cover plate 14, the conductor leg extension and the spacer into the center leg extension 10. Fastened to the center leg by means 2,887,626 Patented May 19, 1959 of screws 16 is a pole piece 17 of magnetic material having a pole face 18.

An armature support 19 is held in position at one end by means of screws 11 passing through cover plate 14 and armature support 19 into the center leg extension 10. The other end of the armature support is held in position by means of screws 20 passing through a terminal board 21, a spacer 22, the armature support 19, a nonmagnetic spacer 23 into the winding support leg 2.

An adjustable pivot 25 on the armature support supports magnetic armature 26 in pivotal relation to the winding leg and the center leg, with a first air gap between the armature and the pole face of the winding leg, a second air gap between the armature and the pole face of the center leg and a third air gap between the armature and the pole face of the bus leg extrusion. The pivot permits the armature to move toward pole face 28 or pole face 13 as the attractive force of the two legs varies. it will be noticed that the air gap at pole face 29 remains essentially the same during armature movement since pole face 29 of the conductor leg is tangent to the arcuate path described by the portion of the armature adjacent to the gap.

A contact support 30 of insulating material is fastened to the armature by any suitable means such as rivets 31. A hardened steel rivet 32 serves as a wear point for adjustable armature stop screw 33. This screw serves as a stop means for the armature and an adjustment for the air gap between the center leg pole face 18 and the armature 26. A threaded sleeve 34 locks the screw in place when the adjustment has been made and prevents vibration from altering the setting of the air gap.

A spacer 35 is fastened to the armature by means of rivets 36. A hardened steel rivet 37 serves as a wear point for adjustable armature stop screw 38. This screw serves as a stop means for the armature and an adjustment for the air gap between the coil support leg pole face and the armature, and has a threaded sleeve 39 which locks the screw in place.

Terminal board 21 is also held in position by means of screws 57 passing through the terminal board 21 and the spacer 22 into the armature bridge. Fastened to the terminal board by means of screw terminals 40 are the fixed contacts 41. A contact bridge 42 of conductive material is fastened to the contact support by means of a screw 24 and nut 43. Fixed contacts 41 are so positioned with respect to the contact bridge 42 that the armature pivotal movement brings the contact bridge into engagement with the fixed contacts and com-. pletes a circuit between screw terminals 40. A protective cover 44 of transparent plastic material is held in position against the terminal board by means of screws 45. Although the contact arrangement is shown as a single bridging contact and two fixed contacts, it will be understood that other contact combinations will work as well.

A winding 46 on the winding leg 2 is supplied with constant voltage direct current through terminals 47 and 48 to provide a reference magnetic flux in the core. A winding support bracket 49 is held in place on the leg by means of a screw 50.

A conductor support bracket 51 of insulating material is afiixed to the conductor support leg by means of bolts.

52 which pass through the bracket into tapped holes in the leg. Bolts 5'3 passing through the support bracket 51, conductor sections 54 and spacers 55 serve to hold the relay in fixed relation to the conductor.

The relay armature 26 is biased against stop screw 33 by means of spring 27. This spring bears against the armature support bracket at one end and against a shoulderon screw 56 which is fastened to the armature. The spring tends to expand and force the shoulder away from the support bracket. This in turn causes the armature to bear against the stop screw 33.

With no current flowing in the conductor or in the constant voltage winding the armature bias spring holds the armature so that the contacts remain open. Energizing the coil with direct current will not actuate the relay since the spring opposes movement of the armature toward the winding support leg and the attractive force of the legs 2 and 3, on opposite sides of the pivot, is approximately equal.

In the case of a forward current flowing in the conductor a magnetic flux is set up in the legs and base member surrounding the conductor. This flux is so polarized, relative to the flux produced by the constant current winding, that the two induced fluxes are in the same direction in the center leg and therefore additive across the air gap between the center leg and the armature. This is the condition shown in Fig. 5. The solid arrows indicate the flux produced by the reference winding and the broken arrows show the direction of the flux produced by the conductor. From Fig. 6 it may be seen that when the two induced fluxes add in the outer leg, they cancel in the center leg. When the center leg has a low value of flux the corresponding air gap will have a low flux density and little attractive force will be exerted on the armature at this point.

The magnetic flux across the air gap between the conductor support leg and the armature causes a force to be exerted on the armature 26 in the direction in which the armature may move. This force does not affect armature movement because of the direction of its application. As a result, the flux in the conductor leg influences armature movement only as it influences the flux density in the winding leg or the center leg.

In the reverse current condition the direction of the flux induced by the conductor is changed. It will be seen from Fig. 6 that this flux induced by the conductor, represented with broken arrows, and the flux from the constant voltage coil, represented with solid arrows, are additive in the coil support leg. That is to say, they have the same polarity within the coil leg 2. This raises the flux density across the air gap between the armature and the coil support leg, and decreases the flux density across the gap between the armature and the center leg. The force of magnetic attraction across the gap between pole face 28 and the armature overcomes the biasing force of the spring, moving the armature towards the winding support leg. This pivotal movement causes the bridging contact to complete the circuit between terminal and terminal.

The center leg is of greater cross sectional area than either of the other two legs. The air gap between the armature and the core support leg is greater than either of the two other air gaps. in the preferred embodiment, the air gap at the core support leg is about twice the other air gaps.

The novel arrangement of the conductor support leg and armature permits construction of an air gap of relatively unchanging dimensions which prevents actuation by heavy overload in the forward direction but does not decrease the sensitivity of the relay. The presence of the fixed air gap prevents a heavy overload current from overcoming the bias force of the spring to cause the relay to actuate. The center leg is made larger than the other legs to insure that it will be the last to saturate. If this were not the case, a heavy current might saturate the center leg causing an attractive force across the air gap between pole face 18 and the armature. However, the force would be limited by the saturation value of the leg. If the current increased further, the attractive force across the air gap at pole face 23 might become sufficiently greater to overcome the limited force across the air gap at pole face 18. Additionally, thearrangernent of the two adjustable air gaps permits adjustment of the reverse current required to actuate the relay and also the amount of reverse current which permits the relay to restore itself to the normal condition. 4

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. An electromagnetic relay, a core of magnetic material comprising: a first leg with a pole face, a second leg with a pole face and a third leg with a pole face: a reference winding and a measuring conductor in magnetic relation to said core; said winding, said conductor and said core so disposed that the flux in said first leg induced by said winding is of the same polarity as the flux induced in the first leg by said conductor when the currents energizing said winding and conductor are of the same polarity, and the flux induced in said second leg by said winding is of the same polarity as'the flux induced in said second leg by said conductor when the currents energizing said winding and conductor are of dissimilar polarity; an armature of magnetic material support means aifixed to said core holding said armature in a spaced pivotal relation to the pole face of said first leg and the pole face of said second leg; the pole face of said third leg disposed in spaced relation adjacent to said armature to maintain the distance between said third leg pole face and said armature substantially constant during pivotal movement of said armature.

2. An electromagnetic relay, a core of magnetic material comprising: a first leg with a pole face, a second leg with a pole face and a third leg with a pole face; a reference winding and a measuring conductor in magnetic relation to said core; said winding, said conductor and said core so disposed that the flux in said first leg induced by said winding is of the same polarity as the flux induced in the first leg by said conductor when the currents energizing said winding and conductor are of the same polarity, and the flux induced in said second leg by said winding is of the same polarity as the flux induced in said second leg by said conductor when the currents energizing said winding and conductor are of dissimilar polarity; an armature of magnetic material support means afiixed to said core holding said armature in a spaced pivotal relation to the pole face of said first leg and the pole face of said second leg for movement toward said first and second leg pole faces in the alternative; the pole face of said third leg disposed tangential to the arcuate path described by the extremity of said armature adjacent to said pole face during pivotal movement of said armature.

3. An electromagnetic relay, a core of magnetic material comprising: a first leg with a pole face, a second leg with a pole face and third leg with a pole face; a reference winding and a measuringconductor in magnetic relation to said core, said winding, said conductor and said core so disposed that the flux in said first leg induced by said winding is of the same polarity as the flux induced in the first leg by said conductor when the currents energi zing said winding and conductor are of the same polarity, and the flux induced insaid second leg by said winding is of the same polarity as the flux induced insaid second leg by said conductor when the currents energizw ingsaid winding and conductorare of dissimilar polarity; an armature of magnetic material, support means affixed to said core holding said armature in a spaced pivotal relation to the pole face of said first leg and the pole face of said second leg whereby said armature is attracted a te a t ward s i fir a d sewed le p i ia e n en sa d s p r means and said r i atu u in a matu ,t 'ar sa d se leg 1; ess, adjustable stop means threadedly mounted onsaid support means abutting said armature at limits of pivotal movement of said armature.

4. An electromagnetic relay comprising a core of magnetic material having a first leg, a second leg, a third leg and a base member connecting said legs at one end in parallel spaced relation, a winding about said first leg, a conductor traversing the space between said second and third legs, a pole face part of said first leg, a pole face part of said second leg, an armature of magnetic material, armature support means afiixed to said core holding said armature in pivotal relation to said core whereby said armature is attracted alternately toward said first and second legs, a first air gap between said armature and said first leg, a second air gap between said armature and said second leg, a third air gap between said armature and said third leg.

5. An electromagnetic relay comprising a core of magnetic material having a first leg, a second leg, a third leg in parallel spaced relation, a base member connecting said legs at one end, said first and third legs having less cross sectional area than said second leg, a winding about said first leg, a conductor traversing the space between said second and third legs, a conductor bracket of insulating material afiixed to said core and said conductor, a pole face part of said first leg, a pole face part of said second leg, an armature of magnetic material, armature support means affixed to said core, pivot means on said support means intermediate said first and second legs holding said armature in pivotal relation 0t said core, a first air gap between said armature and said first leg, a second air gap between said armature and said second leg, a third air gap between said armature and said third leg in a plane tangential to the path of armature movement.

6. An electromagnetic relay comprising a substantially E-shaped core of magnetic material having a first leg, a second leg, a third leg and a base member connecting said legs at one end, a winding about said first leg, a conductor traversing the space defined by said second and third legs, a conductor bracket of insulating material aflrxed to said core and said conductor, a pole face part of said first leg, a pole face part of said second leg, an armature of magnetic material, armature support means affixed to said core, pivot means on said support means intermediate said first leg pole face and said second leg pole face holding said armature in pivotal relation to said core, a first air gap between said armature and said first leg, a second air gap between said armature and said second leg, a third air gap between said armature and said third leg in a plane tangential to the path of armature movement.

7. An electromagnetic relay comprising a substantially E-shaped core of magnetic material having a first leg, a second leg, a third leg and a base member connecting said legs at one end, a winding about said first leg, a conductor traversing the space defined by said second and third legs, a conductor bracket of insulating material afiixed to said core and said conductor, a pole face part of said first leg opposite from the end connected to said base member, a pole face part of said second leg opposite from the end connected to said base member, armature support means afi'ixed to said core, an armature of magnetic material, pivot means on said support means intermediate said first leg pole face and said second leg pole face holding said armature in pivotal relation to said core, a first air gap between said armature and said first leg, a second air gap between said armature and said second log, a third air gap between said armature and said third leg in a plane tangential to the path of armature movement.

References Cited in the file of this patent UNITED STATES PATENTS 2,474,029 Bohn June 21, 1949 2,540,022 Rabenda Ian. 30, 1951 2,735,041 Wurgler Feb. 14, 1956 

